This volume is edited as the proceedings of the international conference 'Iwasawa 2017', which was held at the University of Tokyo from July 19th through July 28th, 2017, in order to commemorate the 100th anniversary of Kenkichi Iwasawa's birth. In total 236 participants attended the conference including 98 participants from 15 countries outside Japan, and enjoyed the talks and the discussions on several themes flourishing in Iwasawa theory. This volume consists of 3 survey papers and of 15 research papers submitted from the speakers and the organizers of the conference. We also included 4 essays on memories of Iwasawa to celebrate the Centennial of Iwasawa's birth. We recommend this volume to all researchers and graduate students who are interested in Iwasawa theory, number theory and related fields.Published by Mathematical Society of Japan and distributed by World Scientific Publishing Co. for all markets except North America